Versatile Dimerisation Process of Translocator Protein (TSPO) Revealed by an Extensive Sampling Based on a Coarse-Grained Dynamics Study.

Translocator protein (TSPO), a mitochondrial membrane protein, has been extensively studied, and its role is still debated and continues to be enigmatic. From a structural perspective, despite availability of atomic structures from different species, the possible oligomeric state and its 3D structure remains elusive. In the present study, we attempted to study dynamics of TSPO from the perspective of oligomerization. In this aim, we examined if and how TSPO monomers could assemble to form a dimer. Accordingly, we performed several coarse-grained molecular dynamics simulations considering two different initial configurations, one with a pair of TSPO monomers distantly placed in a model of a bilayer composed of DMPC/cholesterol mixture and the other with preformed dimer models with different starting interactions. We identify stable TSPO dimers with diverse interfaces, some of which were consistent with earlier experimental observations on putative TSPO oligomer interfaces. For most of the stable ones, interactions between aromatic residues were significantly overrepresented in diverse oligomeric organizations. Interestingly, we identified different communication pathways that involve dimer interfaces. Additionally, we observed that cholesterol molecules in close interaction with the TSPO dimer were able to translocate through the bilayer. This phenomenon might be related to the putative mechanism of cholesterol transport and could be increased and favored by the dimer formation. Overall, our observations shed new light on TSPO oligomerization and bring new perspectives on its dynamics, as well its interactions with protein and ligand partners.